Subroutine */
| 8585 | } /* dladiv_ */ |
| 8586 | |
| 8587 | /* Subroutine */ int dlae2_(doublereal *a, doublereal *b, doublereal *c__, |
| 8588 | doublereal *rt1, doublereal *rt2) |
| 8589 | { |
| 8590 | /* System generated locals */ |
| 8591 | doublereal d__1; |
| 8592 | |
| 8593 | /* Local variables */ |
| 8594 | static doublereal ab, df, tb, sm, rt, adf, acmn, acmx; |
| 8595 | |
| 8596 | |
| 8597 | /* |
| 8598 | -- LAPACK auxiliary routine (version 3.2) -- |
| 8599 | -- LAPACK is a software package provided by Univ. of Tennessee, -- |
| 8600 | -- Univ. of California Berkeley, Univ. of Colorado Denver and NAG Ltd..-- |
| 8601 | November 2006 |
| 8602 | |
| 8603 | |
| 8604 | Purpose |
| 8605 | ======= |
| 8606 | |
| 8607 | DLAE2 computes the eigenvalues of a 2-by-2 symmetric matrix |
| 8608 | [ A B ] |
| 8609 | [ B C ]. |
| 8610 | On return, RT1 is the eigenvalue of larger absolute value, and RT2 |
| 8611 | is the eigenvalue of smaller absolute value. |
| 8612 | |
| 8613 | Arguments |
| 8614 | ========= |
| 8615 | |
| 8616 | A (input) DOUBLE PRECISION |
| 8617 | The (1,1) element of the 2-by-2 matrix. |
| 8618 | |
| 8619 | B (input) DOUBLE PRECISION |
| 8620 | The (1,2) and (2,1) elements of the 2-by-2 matrix. |
| 8621 | |
| 8622 | C (input) DOUBLE PRECISION |
| 8623 | The (2,2) element of the 2-by-2 matrix. |
| 8624 | |
| 8625 | RT1 (output) DOUBLE PRECISION |
| 8626 | The eigenvalue of larger absolute value. |
| 8627 | |
| 8628 | RT2 (output) DOUBLE PRECISION |
| 8629 | The eigenvalue of smaller absolute value. |
| 8630 | |
| 8631 | Further Details |
| 8632 | =============== |
| 8633 | |
| 8634 | RT1 is accurate to a few ulps barring over/underflow. |
| 8635 | |
| 8636 | RT2 may be inaccurate if there is massive cancellation in the |
| 8637 | determinant A*C-B*B; higher precision or correctly rounded or |
| 8638 | correctly truncated arithmetic would be needed to compute RT2 |
| 8639 | accurately in all cases. |
| 8640 | |
| 8641 | Overflow is possible only if RT1 is within a factor of 5 of overflow. |
| 8642 | Underflow is harmless if the input data is 0 or exceeds |
| 8643 | underflow_threshold / macheps. |
| 8644 |